The present invention relates generally to railway vehicles, and, more specifically, to self-steering trucks therein.
In a railway vehicle such as a locomotive, the vehicle body is mounted on a frame which in turn is mounted on a pair of longitudinally spaced apart multi-axle trucks having wheels which ride atop the rails of a train track. The two trucks are typically identical, with each truck having typically two or three axles and a pair of wheels on opposite ends thereof. Disposed outboard of the wheels on the ends of the axles are conventional self-contained bearings in housings which are typically supported in corresponding journal or bearing boxes suspended from the frame by suitable compression coil springs.
In an exemplary three axle diesel-electric locomotive, each axle further includes an integral electrical motor combination, or simply motor combo, for directly powering the wheels. The motor combos drive the wheels for propelling the locomotive either in forward or reverse directions utilizing inherent traction friction between the wheels and the rails. The locomotive, in turn, pulls or pushes a train of railway cars joined thereto. The trucks also include conventional brakes for stopping the locomotive again using the inherent traction friction between the wheels and the rails. Accordingly, traction loads must be carried between the axles and the frame during forward and reverse driving and braking operation. This is conventionally accomplished by suitably suspending the axles to the frame.
However, the axle suspensions must also accommodate vertical motion of the frame relative to the axles as well as limiting longitudinal and lateral translation movements therebetween and yaw rotation of the axles relative to the frame. By restricting the free motion of the axles relative to the frame, improved hunting stability is obtained. Hunting is a conventional term which refers to the uncontrolled lateral and yaw motion of the axles and the truck frame. Hunting often results in lower ride quality, with excess hunting even causing derailment of the locomotive.
Another consideration in locomotive design is the ability of the axles to negotiate curves during operation. In a multi-axle truck, the leading axle negotiates a turn before the trailing axle which creates substantial lateral loading between the axles and the frame and affects efficient operation and longevity of the trucks. In order to accommodate typical problems associated with negotiating rail curves, self steering trucks have been developed. Steering is accomplished by suitably interconnecting the leading and trailing axles so that the axles yaw in opposite directions to each other upon negotiating curves. However, typical train trucks have limited space available for introducing effective self-steering linkage, and conventional self-steering linkages have various degrees of complexity and efficiency in negotiating curves. Furthermore, by allowing the axles to yaw during operation for self-steering, the truck suspension must also allow increased lateral and longitudinal clearances between the axles and the truck frame for allowing a sufficient amount of yaw motion of the axles during curve negotiation. Since the axles are therefore able to move more freely, they are also more prone to undesirable hunting.
Axle suspension design is therefore complex since the axles must be vertically suspended from the frame for accommodating vertical loads; the axles must be longitudinally constrained for carrying the forward and reverse traction loads to the frame; the axles must be also mounted for allowing self-steering yaw motion thereof in opposite angular directions between leading and trailing axles; and, the axles must be laterally constrained. Axle suspension is made even more complex in a three-axle truck since the leading and trailing end axles must be interconnected angularly for self-steering, and the middle axle is independent therefrom and is interposed longitudinally therebetween. Conventional self-steering trucks therefore include a substantial number of pivoting joints which are typically made using conventional bearings or friction joints which are susceptible to wear and fretting problems.
Yet another significant problem in self-steering trucks is the requirement for effecting proper initial alignment between the various axles thereof in order to obtain effective performance during operation. Each axle and corresponding motor combo is a substantially heavy sub-assembly which is typically preassembled into its journal boxes and then assembled together to the truck frame with the corresponding compression springs therebetween. Alignment of the several axles is difficult to accomplish in view of the substantial weight of the sub-assembly which must be manually moved in relatively close proximity to adjacent components of the truck.
Accordingly, it is desirable to effect an improved self-steering multi-axle truck which more effectively utilizes available space for the various components thereof including the self-steering linkage with a reduced number of components thereof and with relatively few joints. Improved self-steering efficiency is also desired along with ease of initial alignment of the axles interconnected by the self-steering linkage.